NAME

       provider-kem - The kem library <-> provider functions

SYNOPSIS

        #include <openssl/core_dispatch.h>
        #include <openssl/core_names.h>

        /*
         * None of these are actual functions, but are displayed like this for
         * the function signatures for functions that are offered as function
         * pointers in OSSL_DISPATCH arrays.
         */

        /* Context management */
        void *OSSL_FUNC_kem_newctx(void *provctx);
        void OSSL_FUNC_kem_freectx(void *ctx);
        void *OSSL_FUNC_kem_dupctx(void *ctx);

        /* Encapsulation */
        int OSSL_FUNC_kem_encapsulate_init(void *ctx, void *provkey, const char *name,
                                           const OSSL_PARAM params[]);
        int OSSL_FUNC_kem_encapsulate(void *ctx, unsigned char *out, size_t *outlen,
                                      unsigned char *secret, size_t *secretlen);

        /* Decapsulation */
        int OSSL_FUNC_kem_decapsulate_init(void *ctx, void *provkey, const char *name);
        int OSSL_FUNC_kem_decapsulate(void *ctx, unsigned char *out, size_t *outlen,
                                      const unsigned char *in, size_t inlen);

        /* KEM parameters */
        int OSSL_FUNC_kem_get_ctx_params(void *ctx, OSSL_PARAM params[]);
        const OSSL_PARAM *OSSL_FUNC_kem_gettable_ctx_params(void *ctx, void *provctx);
        int OSSL_FUNC_kem_set_ctx_params(void *ctx, const OSSL_PARAM params[]);
        const OSSL_PARAM *OSSL_FUNC_kem_settable_ctx_params(void *ctx, void *provctx);

DESCRIPTION

       This documentation is primarily aimed at provider authors. See provider(7) for further
       information.

       The asymmetric kem (OSSL_OP_KEM) operation enables providers to implement asymmetric kem
       algorithms and make them available to applications via the API functions
       EVP_PKEY_encapsulate(3), EVP_PKEY_decapsulate(3) and other related functions.

       All "functions" mentioned here are passed as function pointers between libcrypto and the
       provider in OSSL_DISPATCH arrays via OSSL_ALGORITHM arrays that are returned by the
       provider's provider_query_operation() function (see "Provider Functions" in
       provider-base(7)).

       All these "functions" have a corresponding function type definition named
       OSSL_FUNC_{name}_fn, and a helper function to retrieve the function pointer from an
       OSSL_DISPATCH element named OSSL_FUNC_{name}.  For example, the "function"
       OSSL_FUNC_kem_newctx() has these:

        typedef void *(OSSL_FUNC_kem_newctx_fn)(void *provctx);
        static ossl_inline OSSL_FUNC_kem_newctx_fn
            OSSL_FUNC_kem_newctx(const OSSL_DISPATCH *opf);

       OSSL_DISPATCH arrays are indexed by numbers that are provided as macros in
       openssl-core_dispatch.h(7), as follows:

        OSSL_FUNC_kem_newctx               OSSL_FUNC_KEM_NEWCTX
        OSSL_FUNC_kem_freectx              OSSL_FUNC_KEM_FREECTX
        OSSL_FUNC_kem_dupctx               OSSL_FUNC_KEM_DUPCTX

        OSSL_FUNC_kem_encapsulate_init     OSSL_FUNC_KEM_ENCAPSULATE_INIT
        OSSL_FUNC_kem_encapsulate          OSSL_FUNC_KEM_ENCAPSULATE

        OSSL_FUNC_kem_decapsulate_init     OSSL_FUNC_KEM_DECAPSULATE_INIT
        OSSL_FUNC_kem_decapsulate          OSSL_FUNC_KEM_DECAPSULATE

        OSSL_FUNC_kem_get_ctx_params       OSSL_FUNC_KEM_GET_CTX_PARAMS
        OSSL_FUNC_kem_gettable_ctx_params  OSSL_FUNC_KEM_GETTABLE_CTX_PARAMS
        OSSL_FUNC_kem_set_ctx_params       OSSL_FUNC_KEM_SET_CTX_PARAMS
        OSSL_FUNC_kem_settable_ctx_params  OSSL_FUNC_KEM_SETTABLE_CTX_PARAMS

       An asymmetric kem algorithm implementation may not implement all of these functions.  In
       order to be a consistent set of functions a provider must implement OSSL_FUNC_kem_newctx
       and OSSL_FUNC_kem_freectx.  It must also implement both of OSSL_FUNC_kem_encapsulate_init
       and OSSL_FUNC_kem_encapsulate, or both of OSSL_FUNC_kem_decapsulate_init and
       OSSL_FUNC_kem_decapsulate.  OSSL_FUNC_kem_get_ctx_params is optional but if it is present
       then so must OSSL_FUNC_kem_gettable_ctx_params.  Similarly, OSSL_FUNC_kem_set_ctx_params
       is optional but if it is present then so must OSSL_FUNC_kem_settable_ctx_params.

       An asymmetric kem algorithm must also implement some mechanism for generating, loading or
       importing keys via the key management (OSSL_OP_KEYMGMT) operation.  See
       provider-keymgmt(7) for further details.

   Context Management Functions
       OSSL_FUNC_kem_newctx() should create and return a pointer to a provider side structure for
       holding context information during an asymmetric kem operation.  A pointer to this context
       will be passed back in a number of the other asymmetric kem operation function calls.  The
       parameter provctx is the provider context generated during provider initialisation (see
       provider(7)).

       OSSL_FUNC_kem_freectx() is passed a pointer to the provider side asymmetric kem context in
       the ctx parameter.  This function should free any resources associated with that context.

       OSSL_FUNC_kem_dupctx() should duplicate the provider side asymmetric kem context in the
       ctx parameter and return the duplicate copy.

   Asymmetric Key Encapsulation Functions
       OSSL_FUNC_kem_encapsulate_init() initialises a context for an asymmetric encapsulation
       given a provider side asymmetric kem context in the ctx parameter, a pointer to a provider
       key object in the provkey parameter and the name of the algorithm.  The params, if not
       NULL, should be set on the context in a manner similar to using
       OSSL_FUNC_kem_set_ctx_params().  The key object should have been previously generated,
       loaded or imported into the provider using the key management (OSSL_OP_KEYMGMT) operation
       (see provider-keymgmt(7)>.

       OSSL_FUNC_kem_encapsulate() performs the actual encapsulation itself.  A previously
       initialised asymmetric kem context is passed in the ctx parameter.  Unless out is NULL,
       the data to be encapsulated is internally generated, and returned into the buffer pointed
       to by the secret parameter and the encapsulated data should also be written to the
       location pointed to by the out parameter. The length of the encapsulated data should be
       written to *outlen and the length of the generated secret should be written to *secretlen.

       If out is NULL then the maximum length of the encapsulated data should be written to
       *outlen, and the maximum length of the generated secret should be written to *secretlen.

   Decapsulation Functions
       OSSL_FUNC_kem_decapsulate_init() initialises a context for an asymmetric decapsulation
       given a provider side asymmetric kem context in the ctx parameter, a pointer to a provider
       key object in the provkey parameter, and a name of the algorithm.  The key object should
       have been previously generated, loaded or imported into the provider using the key
       management (OSSL_OP_KEYMGMT) operation (see provider-keymgmt(7)>.

       OSSL_FUNC_kem_decapsulate() performs the actual decapsulation itself.  A previously
       initialised asymmetric kem context is passed in the ctx parameter.  The data to be
       decapsulated is pointed to by the in parameter which is inlen bytes long.  Unless out is
       NULL, the decapsulated data should be written to the location pointed to by the out
       parameter.  The length of the decapsulated data should be written to *outlen.  If out is
       NULL then the maximum length of the decapsulated data should be written to *outlen.

   Asymmetric Key Encapsulation Parameters
       See OSSL_PARAM(3) for further details on the parameters structure used by the
       OSSL_FUNC_kem_get_ctx_params() and OSSL_FUNC_kem_set_ctx_params() functions.

       OSSL_FUNC_kem_get_ctx_params() gets asymmetric kem parameters associated with the given
       provider side asymmetric kem context ctx and stores them in params.  Passing NULL for
       params should return true.

       OSSL_FUNC_kem_set_ctx_params() sets the asymmetric kem parameters associated with the
       given provider side asymmetric kem context ctx to params.  Any parameter settings are
       additional to any that were previously set.  Passing NULL for params should return true.

       No parameters are currently recognised by built-in asymmetric kem algorithms.

       OSSL_FUNC_kem_gettable_ctx_params() and OSSL_FUNC_kem_settable_ctx_params() get a constant
       OSSL_PARAM array that describes the gettable and settable parameters, i.e. parameters that
       can be used with OSSL_FUNC_kem_get_ctx_params() and OSSL_FUNC_kem_set_ctx_params()
       respectively.  See OSSL_PARAM(3) for the use of OSSL_PARAM as parameter descriptor.

RETURN VALUES

       OSSL_FUNC_kem_newctx() and OSSL_FUNC_kem_dupctx() should return the newly created provider
       side asymmetric kem context, or NULL on failure.

       All other functions should return 1 for success or 0 on error.

SEE ALSO

       provider(7)

HISTORY

       The provider KEM interface was introduced in OpenSSL 3.0.

COPYRIGHT

       Copyright 2020-2021 The OpenSSL Project Authors. All Rights Reserved.

       Licensed under the Apache License 2.0 (the "License").  You may not use this file except
       in compliance with the License.  You can obtain a copy in the file LICENSE in the source
       distribution or at <https://www.openssl.org/source/license.html>.